Dual-wavelength lasers with large separation are widely applied in sum-frequency/difference-frequency generation, remote sensing, laser ranging and medical applications. Particularly, dual-wavelength synchronous pulse laser has the advantages of synchronous dual-wavelength pulse output with large pulse energy and high peak power, rendering it with better practical application effects. As compared to conventional solid lasers, fiber lasers get much attention due to their outstanding advantages such as good heat dissipation effect, high conversion efficiency, low threshold, good light beam quality and ease of integration. At present, there are mainly three ways for implementing dual-wavelength synchronous pulse laser output with fiber lasers, which are listed as follows.
1. Dual-wavelength synchronous Q-switching or mode locking is achieved by means of an ion doped gain fiber. Due to the limitation of gain bandwidth, the two wavelengths generated in this way are very close, which limits its application.
2. Dual-wavelength synchronous Q-switching or mode locking is realized by means of two types of gain fibers doped with different ions. These two kinds of gain fibers are located in two different cavities respectively and the two cavities realize dual-wavelength synchronous Q switching or mode locking by using one Q modulator or broadband saturable absorber in common. The two wavelengths generated in this way are far from each other. However, its structure is relatively complex and imposes higher requirements on the manufacturing of the Q modulator or the saturable absorber.
3. A cascading dual-wavelength synchronous pulse laser by means of an ion doped gain fiber. The cascading is transition of laser from a low energy level to an even lower energy level to generate laser of another wavelength. Via this way, transition between two energy levels of the ion is implemented by Q switching or mode locking to generate pulsed laser, in which process the population inversion on the upper level of the additional two levels of the ions is modulated periodically, thereby generating dual-wavelength synchronous pulse laser. However, this is related to factors such as ion doping concentration, doped substrate and cavity parameter. At present, dual-wavelength laser is primarily generated by cascading Holmium- or Erbium-doped fluoride fibers. However, since it is difficult to melt the fluoride fiber with quartz fiber, totally fiber-made lasers are limited, and the method only realizes dual-wavelength synchronous Q-switched, gain switched pulse output with broad pulse width at present.